1. Field of the Invention
The present invention relates to a capacitive-discharging-method ignition apparatus that is utilized in an internal combustion engine.
2. Description of the Related Art
In recent years, the issues such as environment preservation and fuel depletion have been raised; measures for these issues are urgently required also in the automobile industry. The measures include, as an example, ultra-lean-combustion (referred to also as stratified-lean-combustion) operation of an internal combustion engine that utilizes a stratified air-fuel mixture. In the stratified lean combustion, the distribution of inflammable fuel-air mixtures may vary; therefore, in terms of ignition opportunity, long-period spark discharge is required. The concentration of a fuel-air mixture also varies; thus, in some cases, leakage is likely to occur due to a smolder produced through adhesion of carbon to an ignition plug. From these points of view, for the purpose of securely causing a spark discharge even in such a situation where an energy leakage path is created, it is required to generate a large secondary current in the ignition coil unit.
To date, as an ignition apparatus that generates a large secondary current in an ignition coil unit, there exists, for example, a capacitive-discharging-method ignition apparatus disclosed in FIG. 3 of Patent Document 1. In the conventional ignition apparatus, an LC resonance circuit consisting of a large-capacity condenser, a choke coil, and an ignition condenser (referred to as a CDI condenser, hereinafter) is connected with the output of a DC/DC converter; part of electrostatic energy accumulated in the large-capacity condenser is boosted up to a voltage that is approximately twice as high as the output voltage of the DC/DC converter and the CDI condenser is charged with the boosted electrostatic energy, and then the energy accumulated in the CDI condenser is repeatedly supplied to the primary coil of the ignition coil unit, so that intermittent multi-ignition is applied to the ignition plug. In a conventional ignition apparatus disclosed in Patent Document 2, multi-ignition is implemented by providing a plurality of large-scale energy supply units so as to alternately changing the secondary current of the ignition coil unit.